linux-kernel - Re: [PATCH v2] x86/sme: Explicitly map new EFI memmap table as encrypted

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Date:   Wed, 27 Oct 2021 10:11:41 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Ard Biesheuvel <ardb@...nel.org>, linux-efi@...r.kernel.org,
        platform-driver-x86@...r.kernel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Darren Hart <dvhart@...radead.org>,
        Andy Shevchenko <andy@...radead.org>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        stable@...r.kernel.org, linux-kernel@...r.kernel.org,
        x86@...nel.org
Subject: Re: [PATCH v2] x86/sme: Explicitly map new EFI memmap table as
 encrypted

On 10/22/21 12:02 PM, Tom Lendacky wrote:
> Reserving memory using efi_mem_reserve() calls into the x86
> efi_arch_mem_reserve() function. This function will insert a new EFI
> memory descriptor into the EFI memory map representing the area of
> memory to be reserved and marking it as EFI runtime memory.
> 
> As part of adding this new entry, a new EFI memory map is allocated and
> mapped. The mapping is where a problem can occur. This new EFI memory map
> is mapped using early_memremap(). If the allocated memory comes from an
> area that is marked as EFI_BOOT_SERVICES_DATA memory in the current EFI
> memory map, then it will be mapped unencrypted (see memremap_is_efi_data()
> and the call to efi_mem_type()).
> 
> However, during replacement of the old EFI memory map with the new EFI
> memory map, efi_mem_type() is disabled, resulting in the new EFI memory
> map always being mapped encrypted in efi.memmap. This will cause a kernel
> crash later in the boot.
> 
> Since it is known that the new EFI memory map will always be mapped
> encrypted when efi_memmap_install() is called, explicitly map the new EFI
> memory map as encrypted (using early_memremap_prot()) when inserting the
> new memory map entry.
> 
> Cc: <stable@...r.kernel.org> # 4.14.x
> Fixes: 8f716c9b5feb ("x86/mm: Add support to access boot related data in the clear")
> Acked-by: Ard Biesheuvel <ardb@...nel.org>
> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>

Ard, are you going to take this through the EFI tree or does it need to go 
through another tree?

Thanks,
Tom

> 
> ---
> Changes for v2:
> - Update/expand commit message to (hopefully) make it easier to read and
>    understand
> - Add a comment around the use of the early_memremap_prot() call
> ---
>   arch/x86/platform/efi/quirks.c | 14 +++++++++++++-
>   1 file changed, 13 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c
> index b15ebfe40a73..14f8f20d727a 100644
> --- a/arch/x86/platform/efi/quirks.c
> +++ b/arch/x86/platform/efi/quirks.c
> @@ -277,7 +277,19 @@ void __init efi_arch_mem_reserve(phys_addr_t addr, u64 size)
>   		return;
>   	}
>   
> -	new = early_memremap(data.phys_map, data.size);
> +	/*
> +	 * When SME is active, early_memremap() can map the memory unencrypted
> +	 * if the allocation came from EFI_BOOT_SERVICES_DATA (see
> +	 * memremap_is_efi_data() and the call to efi_mem_type()). However,
> +	 * when efi_memmap_install() is called to replace the memory map,
> +	 * efi_mem_type() is "disabled" and so the memory will always be mapped
> +	 * encrypted. To avoid this possible mismatch between the mappings,
> +	 * always map the newly allocated memmap memory as encrypted.
> +	 *
> +	 * When SME is not active, this behaves just like early_memremap().
> +	 */
> +	new = early_memremap_prot(data.phys_map, data.size,
> +				  pgprot_val(pgprot_encrypted(FIXMAP_PAGE_NORMAL)));
>   	if (!new) {
>   		pr_err("Failed to map new boot services memmap\n");
>   		return;
>